Can I build an ADU in Walpole, Massachusetts?
Yes. Walpole's zoning bylaw allows one accessory dwelling unit (ADU) by right on a single-family lot in the Rural, Residence A, Residence B and General Residence districts, up to 900 sq ft or half the main home's floor area, whichever is smaller. You need a building permit; a detached ADU also goes through Limited Site Plan Review with the Building Commissioner, and short-term rentals of the ADU are prohibited.
| ADUs allowed per lot (by right) | 1 [1] |
| Districts where allowed by right | RA, RB, GR and R (Rural); prohibited in PSRC and business/industrial districts [2] |
| Maximum size | 900 sq ft or 1/2 the principal dwelling's floor area, whichever is smaller [3] |
| Entrance for attached ADU | Side or rear of the main house [4] |
| Parking | No more than 1 space for the ADU; none if within 0.5 miles of a commuter rail or bus station [6] |
| Short-term rental of the ADU | Prohibited [5] |
| Detached ADU review | Limited Site Plan Review (abutter comments within 21 days) [7] |
Where and how many
Section 5-B.2 of the zoning bylaw lets you build or create one ADU "as a matter of right" on a lot with a principal dwelling in any single-family residential district [1]. The use table marks ADUs as allowed (A) in the Residence A, Residence B, General Residence and Rural districts and prohibited (X) elsewhere [2]. The ADU must be a complete housekeeping unit with sleeping quarters, kitchen, bath and laundry.
Size and design
The definition caps an ADU at half the floor area of the main home or 900 square feet, whichever is smaller, and requires a separate entrance that meets the building code for safe egress [3]. An attached ADU's outside entrance must be on the side or rear of the main house [4]. The ADU must meet the district's normal setbacks and dimensional rules, and the bylaw does not require the owner to live on the property.
Parking and rentals
The bylaw requires no more than one off-street parking space for the ADU, and none if the ADU is within 0.5 miles of a commuter rail or bus station [6]. Short-term rentals within the ADU are prohibited [5]; longer-term leasing is not restricted in the text.
Detached ADUs
A detached ADU (for example a garage apartment or backyard cottage) goes through Limited Site Plan Review. You must notify immediately adjoining abutters by certified mail when you file, and they have 21 days to comment to the Building Commissioner [7]. The review checks screening of parking or storage within 15 feet of a lot line, glare from lighting, placement of decks and patios, screening of trash areas, and the orientation of any upper-story balcony.
Permits
No ADU may be built or converted until the Building Commissioner issues a permit, and a Board of Health sewage disposal permit comes first where one applies [8]. Most of these local rules match the state ADU law shown on this page: by-right approval, no owner-occupancy rule, a one-space parking cap, and a short-term rental ban, which state law allows. Two provisions are less certain. State law lets towns use reasonable site plan review and design rules, but the side-or-rear entrance rule for attached ADUs and the abutter-comment step for detached ADUs apply only to ADUs, and if they were found unreasonable under the state regulations (760 CMR 71.00), state law may override them.
See how Walpole compares with 8+ other Massachusetts towns on accessory dwelling units (adus) →
Next steps
- Check your zoning district (RA, RB, GR or R) on the town zoning map; ADUs are not allowed by right elsewhere.
- Confirm the ADU fits within 900 sq ft and half the main home's floor area, and meets the district's setbacks.
- If you are on septic, get the Board of Health sewage disposal permit first.
- Apply to the Building Department (Inspectional Services, Town Hall, 508-660-6348) for a building permit; for a detached ADU, also file for Limited Site Plan Review and send certified-mail notice to abutting neighbors.
Common questions
- Are ADUs allowed in Walpole, Massachusetts?
- Yes. Walpole's zoning bylaw allows one accessory dwelling unit by right on a single-family lot in the Rural, Residence A, Residence B and General Residence districts. ADUs are prohibited in other districts, and the owner does not have to live on the property.
- How big can an ADU be in Walpole, Massachusetts?
- An ADU can be no larger than 900 sq ft or half the main home's floor area, whichever is smaller. It must also meet the district's normal setbacks and dimensional rules.
- Do I need a permit to build an ADU in Walpole, Massachusetts?
- Yes. You need a building permit from the Building Commissioner, and a Board of Health sewage disposal permit comes first where one applies. A detached ADU also goes through Limited Site Plan Review, with certified-mail notice to abutters, who have 21 days to comment.
- Can I rent my ADU on Airbnb in Walpole, Massachusetts?
- No. Short-term rentals within an ADU are prohibited under Walpole's zoning bylaw. Longer-term leasing is not restricted in the bylaw text.
- How much parking does an ADU need in Walpole, Massachusetts?
- No more than one off-street parking space can be required for the ADU, and none if it is within 0.5 miles of a commuter rail or bus station.
Massachusetts' statewide ADU law
Since February 2, 2025, the Affordable Homes Act (St. 2024, c. 150, §8) has protected one accessory dwelling unit (ADU) per lot in any zoning district that allows single-family homes (M.G.L. c. 40A, §3). Your town cannot ban it, require a special permit or other discretionary approval, or "unreasonably restrict" building or renting it.
What counts as a protected ADU:
- A self-contained unit with its own sleeping, cooking and bathroom facilities, on the same lot as the main home.
- No larger than 900 sq ft or half the main home's floor area, whichever is smaller.
- It can be attached or detached, and it needs a separate entrance that meets the building code.
What towns cannot require:
- That the owner live in the main home or the ADU.
- More than 1 extra parking space, or any extra space if the lot is within 0.5 miles of a subway, commuter rail, ferry or bus station.
- A minimum lot size, caps on the number of ADUs, or limits on who may live there (age, income, relationship).
What towns can still do: use reasonable site plan review, setback, height and bulk rules, require Title 5 septic compliance, and restrict or ban short-term rentals of ADUs. A second ADU on the same lot needs a special permit. State regulations at 760 CMR 71.00 (in effect since January 31, 2025) explain which rules count as unreasonable.
What the bylaw says
- Sec. 5-B.2.3, Use and Regulations, Zoning Bylaws (Revised Through October 2025), p. 28
In all single-family residential zoning districts, one ADU may be constructed or established as a matter of right on the same lot as a principal dwelling provided the following conditions are met:
- Table 5-B.1, Use Table, 3.w, Zoning Bylaws (Revised Through October 2025), p. 21
w. Accessory Dwelling Unit4 A A A A X X X X X X
- Sec. 14, Definitions (Accessory Dwelling Unit), Zoning Bylaws (Revised Through October 2025), p. 104
(i) maintains a separate entrance, either directly from the outside or through an entry hall or corridor shared with the principal dwelling sufficient to meet the requirements of the state building code for safe egress; and (ii) is not larger in floor area than 1/2 the floor area of the principal dwelling or 900 square feet, whichever is smaller;
- Sec. 5-B.2.3.D, Zoning Bylaws (Revised Through October 2025), p. 28
Any outside entrance serving an attached accessory dwelling unit shall be located on the side or rear of the principal dwelling unit.
- Sec. 5-B.2.3.G, Zoning Bylaws (Revised Through October 2025), p. 28
Short-term rentals within the accessory dwelling unit are prohibited.
- Sec. 5-B.2.3.I, Zoning Bylaws (Revised Through October 2025), p. 28
Off-street parking shall be provided for use by all occupants of both the principal and accessory dwelling units, provided not more than one (1) parking space shall be required for an ADU, but if the ADU is located within 0.5 miles of a commuter rail station or bus station, no additional parking space shall be required for the ADU.
- Sec. 5-B.2.4.A(3), Zoning Bylaws (Revised Through October 2025), p. 29
The applicant shall notify abutters immediately adjoining the subject property by certified mail immediately upon filing an application for Limited Site Plan Review. Said notice shall inform abutters that any comments regarding the application may be provided to the Building Commissioner within twenty-one (21) days of the date the application was filed.
- Sec. 5-B.2.5.B, Zoning Bylaws (Revised Through October 2025), p. 29
No permit shall be issued until a sewage disposal works permit, when applicable, has first been obtained from the Board of Health and the proposed building and location thereof conform with the town’s bylaws.